Sr—Nd Isotopic Disequilibrium of Clinopyroxenes from the Ultrapotassic Effusive Rocks of the East African Rift System: Mixing of Melts and Source Heterogeneity

摘要

Ultrapotassic magmatism is the deepest type of magmatism showing a number of indicators of mantle source enrichment in incompatible trace elements [1]. The western branch of the East African rift system is a classic area of the occurrence of ultrapotassic rocks [2, 3]. The presence of rocks with different modal and chemical compositions within a relatively small area reflects kilometer-scale heterogeneity in the upper mantle. The most popular model for the source of potassic magmas is a lherzolitic (harzburgitic?) mantle with numerous pyroxenite veins and layers [4]. Additional evidence for the heterogeneity of the source of potassic magmas in the western branch of the rift was obtained during the investigation of Sr and Nd isotopic systematics in phenocrysts from the volcanic rocks.